Interpretive Summary: Insecticide resistance significantly reduces the ability to control German cockroach populations. Detection of insecticide resistance before treatments are chosen and dispensed would improve control and eliminate inappropriate insecticide applications. A scientist at the Center for Medical, Agricultural and Veterinary Entomology, Gainesville, Florida has attempted to use surrogate substrates (non-insecticides) to identify metabolic resistance mechanisms in the German cockroach. Although oxidative and conjugative detoxication enzymes were elevated in resistant German cockroaches, no direct relationship between resistance level and enzyme activity levels were observed. However, hydrolytic enzyme activity correlated well with pyrethroid and carbamate insecticides. These results indicate that hydrolytic enzymes may be a useful insecticide resistance monitoring tool in German cockroaches.

Technical Abstract:
Topical bioassays with cypermethrin, -cyhalothrin, permethrin, propoxur, and chlorpyrifos were conducted on twelve German cockroach strains recently collected from the field. Resistance levels ranged from 3- to 159-fold for cypermethrin, 2- to 88-fold for permethrin, 4- to 55-fold for - cyhalothrin, 5- to 33-fold for propoxur, and 3- to 19-fold for chlorpyrifos. The synergists piperonyl butoxide (PBO) and S,S,S- tributylphoshorotrithioate (DEF) affected cypermethrin resistance to varying degrees depending on the strain. Piperonyl butoxide pretreatment decreased cypermethrin resistance in only 5 strains, but caused an increase in resistance level in 7 strains. Conversely, DEF pretreatment reduced the resistance level in 10 of the strains and increased the resistance level in only 2 strains. Correlation analysis of resistance ratios for each strain and insecticide indicated a direct relationship between resistance level of fone insecticide and another, especially among the pyrethroids. All field strains exhibited significantly higher microsomal oxidase, glutathione S- transferase and esterase activities toward surrogate substrates as compared with the insecticide susceptible strain. However, levels of cytochrome P450 content, aldrin epoxidase activity, methoxyresorufin O-demethylase activity, and glutathione S-transferase activity were not correlated with pyrethroid resistance suggesting that these activities are poor indicators of pyrethroid resistance. Interestingly, significant correlations were found between general esterase activity and cypermethrin (P = 0.002), permethrin (0.007), cyhalothrin (0.002), and propoxur (0.001) resistance levels. The data support the conclusion of esterase involvement in cypermethrin resistance determined by synergist (DEF) bioassay.